Process of coating metal surfaces



-Patented Jan. 21, 11942 UNITED STATES PATENT :OFFICE PROCESS OF COATINGMETAL SURFACES Cecil J. MacKay, Montreal, Quebec, Canada, as-

. signor to Rust Proofing,

Company of Canada,

Limited, Montreal, Quebec, Canada, a corpora tion of Canada No Drawing.'ippuaaonm, 14, 1939, Serial No. 284,557. In Canada August 13, 1935 16Claims. (CI. 148-6) This invention relates broadly to the treatment ofmetal articles for the preparation of the metal surfaces to resistrusting or corrosion and to recel've surface coatings of various sortsand in some cases for Sthe improvement of characteristics tion is acontinuation in part ofmy prior application Ser. No. 36,217, filedAugust 14,.1935, re- "sulting in Patent 2,244,526, June 3, 1941.

The primary object of the invention is to pro,- vide a process oftreating surfaces of iron, steel, ferrousalloys, copper and cuprousalloys to render themresistant to rusting; oxidation and cor rosionand'better adapted to receive and-retain surface coatings such as paint,lacquer and nonimmersing the articles to be treated in baths of .-of themetal articles, and the present applicavitreous enamels (either naturalor synthetic resin or celluloslc): vitreous enamels and all manner ofmetal coatings whether deposited electrolytically or by hot dipping,rolling, tumbling or spraying processes.

Another object is to provide a process of imparting to metal articles aflnish'which does not interfere with electric or acetylene welding or 1brazing and which serves to diminish or inhibit electrolytic actionbetween different metals.

' Various other objects and the advantages of the invention may beascertained from the following description.

In its broadest aspect, the invention comprises,

firstly, subjecting the articles to be treated to. the action of amolten coating agent comprising an alkali metal phosphate or mixture ofalkali metal phosphates with the addition of one or more of the alkalimetal nitrates, and, if desired, with the further addition of alkalimetal carbonate. To any of these mixtures therevmay be added an oxygencarrying agent, a fluxing agent or a stabilizing agent; secondly,treating the articles with a neutralizing solution and thirdly andoptionally treating the articles with a-colouring, sealing andfinishingsolution. The articles may bewashedwith water as may be desired ornecessaryw between the several treatments.

More particularly, the invention comprises the features and combinationsof featuresherein (118- closed together with all such modificationsthereof and substitutions of equivalents therefor as are within thescope of the appended claims.

The treatment is effected fnost conveniently by stripping and coat- Themolten bath is'composed essentially of an alkali metal phosphate ormixture of alkali metal phosphates in admixture with one or more ofthe.alkali metal nitrates, and hydroxides, and if desired, alkali metalcarbonate, with or without b'ath fluxing, or stabilizing agents, orboth. For treating iron, steel and ferrous alloys, it is preferred thatthe predominant constituent of the bath be a mixture of alkali-metalphosphate,

with one or more of the alkali metal nitrates and possibly alkali metalcarbonate, and that the alkali metal hydroxides, if used at all, bepresent 'in minor proportion; but for treating copper,

brass and bronze, it is preferred that alkali metal phosphate ormixtures thereof with alkali metal nitrate or nitrate and carbonate, andan alkali metal hydroxide or mixture of alkali metal hydroxides bepresent'in about equal proportions.

Thus, for treating iron, steel and ferrous alloys,

66% or more of the molten bath is preferably,

composed of mixtures of alkali metal phosphate with one or more of thealkali metal nitrates and carbonates and the remainder, being 34% orless,

' is composed of one or more of the alkali metal The invention isprimarily intended to provide a durable and attractive surface finish onferrous and cuprous and aluminous metallic articles, in-

dependently of any other. surface coating and which-flnish is resistantto rusting, oxidation and corrosion oi the metal'and forms an improvedfoundationfcr other surface coatings.

hydroxides. .For treating copper and its alloys, the bath is composedpreferably of about of a mixtureof alkali metal phosphate with one ormore of the alkali metal nitrates and carbonates and about 50% of alkalimetal hydroxide. The addition of a small proportion of manganese dioxide.or crystalline copper sulphate asa fliix improves the fluidityof thebath and thus reduces the loss-through dragout on the articles treated.

The manganese dioxide has oxidizing andalso catalytic or acceleratingaction. The amount of either manganese dioxide or copper sulphate shouldbe between 0.5% and 10% of the bath and preferably is about.1% or 2%.Copper sulphate appears also to have a stabilizing effect on the bath,especially at higher temperatures.

n it is desired'to impartthe most eflective rust and corrosion retardingfinish to the surface of" the metal, the bath temperature should'bebetween 500, and 900 preferably between The actual temperature used-700" and 900 F. depends upon the composition of the bath, the metaltreated and the duration of the treatment,

which last .dependsup'on the: necessity, or otherof first removingrid-existing coating. As

the duration of treatment depends to someextent on the temperature; thenature of the articles immersed .will have some. influence. Thus,comparing a compactcasti'ng. and a thin plate of equal it is preferredthat they be transferred to a finishing bath, preferably after washingto remove any free acid from the surface thereof. This finishing bath iscomposed of iron sulphate,crystalline haematoxylin, water solublenigrosine, tannic acid or other suitable sealing or colouring agent insolution in water. The bath is made up with "any of the .above'ingredients present in proportion of: approximately 4 ounces to 1imperial surface areas',-the casting will'require somewhat longerimmersioni on account of heat loss from the bath to the'casting- Themolten bethegreaets,

integral with the metahwhich is an excellent retardant of rust andcorrosion. This coating is so thin it does notcause any significantincrease in the dimensions of the articles treated. Screws or bolts withvery fine threads are not appreciably tighter .in cooperating tappedholes after treatmentthan before treatment. Thin steel sheets treated asdescribed may be bent back and r forth at: small radius curvature withno apparent detriment to the surface finish until about the timefracture of the metal occurs.

quer, non-vitreous and vitreous enamels and w n I withthemetaltopro--duce a very strongly-adherent coating practically The coating .is',moreover, a better foundation for paint, lacis'maintained preferably ata temperature of approximately 180 F., but the temperature may be loweror higher, for example between 100 and 200' F'.; and the articles areimmersed therein for .two to ten minutes and then removed and washedwith' water. The resulting finish is more resistant .to rust andcorrosion than that proued-mthe first bath and is a better base forpaint, enamel and metal plating. The finish is 'ofuvery good appearance,ranging from gun meta to dark blue or black. If given a coat ofoil"or"fclear lacquer, the appearance is similar to good blackf'e namel.In addition to colouring the metal plating such as zinc, tin, cadmium,copper, i

nickel, and the like (electrolytic, hot dip, tumbled or rolled) than themetal of the article itself and such surface coatings applied toarticles treated according to this invention are more adherent than whenapplied to bare metal.

Articles to be treated in the molten bath are merelyimmersed therein andno agitation of the articles or of the bath is necessary. The materialof the bath is very penetrating and goes into the most -min'utecrevices. Metal plates closely packed together'receive as good a finishon the contact surfaces as on exposed surfaces and do not show-anytraces of the contact such as would occur in electroplating or afterdipping in paint or enamel. Small articles such as bolts, nuts, washersand the like may be treated in bulk in baskets.

After immersion in'the molten bath, the are finish im orted in the firstbath,'the materials used enter the pores or intermolecular spaces of thefinishandseal the same against entrance of rust or corrosionproducingagents;

The neutralizing bath is very important if a paint, lacqur- 1or enamelis to be, applied subsequentlyasfevery trace of alkali must be removedto avoid'jthe: appearance of blemishes in the final coating.

'. .The condition;iof the second and third baths "shouldbe tested; fromtime to time as to acidity 'andalkalinity and adjusted as necessary byaddition of acid or other ingredient to correct the condltiom. rSteel-articles which have been tempered or case hardened may be treatedaccording to this invention withoutfafiecting the temper or hardness.Also, the finish imparted does not interfere with electric .or acetylenewelding or brazing.

Specific examples of various molten bath formulae are given below but itwill be understood ticles are lifted out, drained for a :few'seconds andthen washed with water either by immersion therein or by spraying. Thewashing should be more thorough if the molten bath contains a largepercentage of sodium or potassium hydroxide than if it contains only alittle or none at all.

The'washed articles are next immersed in a neutralizing bath being aweak aqueous solution of hydrochloric, sulphuric, oxalic or othersuitable acid or an'aqueous solution of iron sulphate, maintainedpreferably at a temperature of-about 160" F., but the temperature may belower or higher, for example, from 100 to 200 F. 'A 1% boring to themetal but darkens and improves the appearance ofthe finish impartedinthe molten After treatment in the neutralizing bath, the articles may bedischarged and used as they are or may be painted, enamelled or metalplated, but

materials or proportions of the examples.

' Fmsr Bun Example I Trlsodium phosphate i. 3 Potassium nitrate 2 s amp1e11 Trisodiu m phosphate 3 .Sodium hydroxide v 2 n '1 Example IIITrlso'dium phosphate r' 4 Potassium nitrate 1 Sodium hydroxide. 1

Example'IV Trisodium phosphate-""4"; 4 Sodium carbonate 1 Sodiumhydroxide 2 Example V' Triaodium phosphate 2 Potassium phosphate 2 theinvention is not in any way limited to the Sodium hydroxide 4 Inpreparing amr of the molten baths it is essential to first melt thenitrate or hydroxide or mixturethereof and then add thephosphategradually holding the bath temperature as low as possible until all thephosphate has been added and meltedinto the bath. To any of theforegoing mixtures'there may be added, 11 desired, from 0.5% to 10% ofmanganese dioxide v airman v 3 Example?! I mfinish and moreresistanarflt to rust and cor- Trisodium h t v on 18 0d 18 0188 1n m u gg f g the third bath also. It is usually preferable to sodium 3 use ironsulphate in one only of the baths, that sodiumhbdmnde 2 is, if it isused in the second bath one of the v other agents is used in the thirdbath, but if Example Vlf the sulphate is to be used in the third bath,the modlum h t 2 second 9 3 7 d with y Potassium nitrate 3 chloflc other10 .Having thus described my invention, what I ExampleV III laim is: an:4 A process 0 coa articles of iron, copper, g gfi fi g g g "f 'f""" gand alloys of each of -them, which process come prises fusing togethera-mixture, of alkali metal Example IX colgfiounds infiludlng alkalimetal phosphate and v a metal trate, the resulting mixture being fgg fi5 g in the molten state reactive with the metal treatfi g 1 ed toproduce a coating thereon, and subjecting um hy r9 5 the articles totheaction of the molten mass. 1

Example X ,20 2. A process of coating articles of ironfcop per, andalloys of each of them, which process ggg g gl g grgg t f comprisesfusing together a mixture' alkali sodium by dr on 3 metal compoundsincluding alkali me 'phosphate and alkali metal hydroxide, the resultingExample XI g5 mixture being in the molten state reactive with the metaltreatedrto produce a coating thereon, 3.333% $31 22? *"f f 2 andsubjecting the articles to the action of the molten mass.

Potassium hydroxide "-""':"-"'-'""T 3. A process of coating articles ofiron, copper, x mp e XII and alloys of each of them, which processcommodmm phosbhatg 50 prises fusing together a mixture of alkali me alSodium hydroxide 50 compounds including alkali metal phosphate, al-

kali metal nitrate and alkali metal hydroxide, the

, resulting mixture being in the molten state reacor crystalline coppersulphate as afiuxing and stabilizing agent, the preferred amount being lto 2%.

In any of the foregoing examples, the alkali metal compounds named maybe replaced by the 1 similar compound of the other alkali metal.

Instead of trisodium phosphate, there may be substituted any of theother sodium phosphates,

but trisodium phosphate is preferred on account of its melting point andready miscibility in the invention, and especially that resulting fromimtive with the metal treated to-prbduceja coating thereon, andsubjecting the articles to the action of the molten mass. 3

. 4. A process ef coating articles of iron, copper, and alloys of eachofthem', which process comprises fusing together a mixture of alkalimetal compounds including alkali metal phosphate, al

kali metal carbonate and alkali metal hydroxide, the resulting mixturebeing in the molten state reactive with the metal treated to produce acoating thereon, and subjecting the articlesto the action of the moltenmass.

r 5. A process of coating articles of iron, copper, and alloys of eachof them, which process comprises fusing together a mixture of alkalimetal compounds including alkali metal phosphate, al-

i kali metal nitrate and alkali metal carbonate, the

mer sion in all three baths, is very durable and tenacious, so thatmetal sheets thus treated may be formed in dies without injuring thefinish.

The finishing treatment, especially when temperatures between 600 and900 E. are used, has an annealing effect which improves the strength ofthe metal. In certain cases where annealing isrequired between formingoperations, the parts may be treated according to this invention betweenthe forming operations and annealing thus effected simultaneously withsurface finishing. It is possible also .to heat the bath above 900 F.,say to l200 or even' bath may be omitted, but a better appearing Initrate.-

resulting mixture being in the molten state reactive with the metaltreated to produce a coating thereon, and subjecting-the articles toth'e action of the molten mass.

6. A process accor ing to claim 1 in which the mixture has added to itnganese dioxide.

7. A composition of matter for use as a molten bath in surfacecoatingferrous and cuprous articles comprising the product resultingfromfusingtogether a mixture of alkali metal compounds including alkali metalphosphate and alkali metal 8. Acomposition of matter for use as a moltenbath in surface coating ferrous and cuprous articles comprising theproduct resulting from fusing together a mixture of alkali metalcompounds including alkali metal phosphate and alkali metal hydroxide.

9. Ferrous and cuprous articles having on the surface and' in the poresthereof axtenaciously adhering rust and corrosion resisting coatingproduced by subjectingthe articles to the action of a molten massresulting from fusing together alkali metal phosphate and alkali metalnitrate.

10. lferrous and cuprous articles having on the surface and in the poresthereof a tenaciously adhering rust and corrosion resisting coating pro-.duced.by subjecting the articles to the action of a molten massresulting from fusing together a mixture of alkali metal compoundsincluding'alkali metal phosphate and alkali metal hydroxide 11. Theprocess for producing a protective coating on ferrous, rust susceptiblemetallic surfaces which consists in subjecting such surfaces to a moltenbath consisting of hydroxide and a phosphate.

12. The process for producing a protective coating on ferrous, rustsusceptible metallic surfaces that consists in subjecting such surfacesto a molten bath consisting of sodium nitrate, sodium hydroxide, and aphosphate.

13. The process for producing a protective coating on ferrous, rust.susceptible metallic surfaces which consists in subjecting such surfacesto a molten bath composed of chemicals including hydroxide and aphosphate.

a mixture of alkali metal compounds including 14 The process forproducing a protective coating on ferrous, rust susceptible metallicsurfaceswhlch consists in subjecting such surfaces to a molten bathconsisting of'hydroxide, an oxi-v dizer' and a phosphate.

15. A-process of coating articles of iron, copper, and alloys of each ofthem, which process. comprises fusing together a mixture of alkali metalcompounds including alkali metal phosphate as the essential ingredientand manganese dioxide, the resultingmixture being in the molten statereactive with the metal treated to produce a strongly adherent coatingthereon, and subjecting the articles to the action of the molten mass.

16.-A process of coating articles of iron, copper, and alloys of each ofthem, which process comprises fusing together a mixture of alkali metalcompounds including trisodium phosphate as the essential ingredient, theresulting mixture being in the'molten state reactive with the metaltreatedto produce a srongly adherent coating thereon, and subjecting thearticles to the action of the molten mass.

QECIL J. MACKAY.

